U.S. Pat. No. 4,777,580 to D. Bingham shows a full wave rectifier circuit having a mix of bipolar and MOS transistors arranged in a bridge configuration.
U.S. Pat. No. 4,139,880 to R. Ulmer et al. discloses two p-channel MOS transistors and two n-channel MOS transistors interconnected in a circuit, similar to a full wave bridge, but providing a polarity reversal circuit.
FIG. 1 shows a prior art bridge circuit in which four n-channel MOS transistors 11, 13, 15 and 17 are employed in a full wave bridge configuration. An alternating current input is received at terminals 21 and 23. When terminal AC1 is positive, transistors 11 and 15 are in the "on" condition and transistors 13 and 17 are "off" or in a non-conducting state. The output terminal 31, V.sub.DD, Will charge to the voltage of AC1 minus the threshold voltage of transistor 11 and an IR drop across transistor 11 which is dependent upon the amount of current required by V.sub.DD. Output terminal 33, V.sub.SS, will charge to the value of input terminal 23, AC2, minus the IR drop across transistor 15. When the opposite state of the alternating current input signal is placed across input terminals 21 and 23, i.e. AC2 is more positive than AC1, then transistors 13 and 17 are on and transistors 11 and 15 are off. Under these conditions, output terminal 31, V.sub.DD will charge to the voltage of AC2 minus the threshold voltage of transistor 13 and the IR drop across transistor 13 depending upon the current required by the output signal V.sub.DD. Also, V.sub.SS will charge to the value of AC1 minus an IR drop across transistor 17. The circuit of FIG. 1 will give a full wave rectified signal between the output terminals 31 and 33. A filtering capacitor has been connected in the prior art between the terminals 31 and 33 in order to provide a rectified power signal.
In the prior art, a rectifier circuit of FIG. 1 has been used in a circuit of the type shown in U.S. Pat. No. 5,166,676 to T. Milheiser. In this patent an inductive input receives radio frequency energy which is fed into a coil which is disposed across the inputs of a full wave rectifier. This is shown schematically in FIG. 2 where a first transmitting circuit 35 has an antenna 37 which radiates radio frequency energy 39 to a remote passive integrated transponder 41 which includes a coil 43, a rectifier 45, similar to the one described in FIG. 1 above, and a filter capacitor 47 which smoothes ripples in the rectified radio frequency signal. The smoothed DC voltage is fed to a utilization circuit 49.
One of the problems encountered in the prior art is that the rectifier circuit of FIG. 1 will break down if input voltages exceed transistor breakdown voltages. One remedy might be to place more transistors in the rectifier circuit to distribute high voltage loads. A problem with this approach is an increased circuit complexity. An object of the invention was to devise a compact full wave rectifier having high voltage characteristics and an associated power supply circuit.